1. Field of the Invention
This invention relates to chemical compositions based upon rosin and reaction products of rosin with other substances and is concerned, in particular, with chemical compositions which are made from stable dispersions of rosin or rosin-based products and which are themselves in the form of stable dispersions. The invention also relates to processes of manufacture of the chemical compositions of the invention and to processes employing these chemical compositions, such as the sizing of paper.
2. Description of the Prior Art
Stable dispersions of rosin or rosin-based products are well-known and have long been used, especially as sizing agents in the manufacture of paper. In this specification, the term "paper" is used, for convenience, to mean all forms of paper, paperboard and related products whose manufacture involves the employment of a sizing agent upon cellulosic or other fibres. Paper sizing agents are usually employed either by being added to the cellulosic or other fibre stock from which a web is later made or by being applied to the surface after the web has been formed. Rosin-based sizing agents depend for their sizing upon the formation of electrostatic bonds between the sizing agent and the cellulosic or other fibres of the paper stock or web. Highly efficient sizing agents developed more recently include many kinds which, in use, form chemical bonds and thus are known as "reactive" sizing agents. A major development in the paper sizing art was the discovery that reaction products formed by rosin or unsaturated compounds present in rosin, on the one hand, and unsaturated carboxylic acids or their anhydrides on the other hand, especially maleic or furmaric acid or maleic anhydride, have greatly enhanced sizing efficiency, as compared with sizing agents which are essentially dispersions of rosin itself. These so-called "maleated" rosin reaction products and other related sizing agents are rather expensive to make and so they were often used to fortify conventional rosin dispersions, rather than to replace them, and the resultant compositions are commonly known as "fortified sizing agents".
In practice, all types of paper sizing agents are usually in the form of stable dispersions and they cause sizing by depositing rosin-based or other materials on to the fibre stock or the paper web, so that sizing essentially involves breaking the stable dispersion. This can occur on contact between the emulsion and the stock or web, where the latter is effective to destroy the stability of the dispersion. Usually, however, adequate sizing does not arise from mere contact of the paper sizing agent with the paper stock or web and requires the presence of an added reactant to break the dispersion and so cause the desired deposition of sizing components on the fibres of the paper stock or web. By far the commonest agent used is aluminum sulphate, i.e. papermaker's alum, which is particularly efficient, both because of its acid character and because of the effectiveness of the aluminum ion as flocculant. In fact, the majority of sizing agents in use will remain stable in the presence of cellulosic fibres, but will be destabilized in the presence of alum, because the latter is much more reactive than cellulose.
As a consequence of this, a considerable degree of skill has to be exercised in the manufacture of paper, so as to ensure that the stock, the sizing agent and the alum are brought together in the requisite proportions and under such conditions as to effect optimum sizing. In particular, difficulty can arise in ensuring that the correct amount of alum is added, in accordance with the nature and properties of the particular stock and the particular sizing agent in use. Instead of having to add at least two materials to the paper-making stock, namely the sizing agent and alum, it would obviously be of considerable benefit if the sizing agent and the alum or, in general, all the materials which need to be added to the stock, could be combined into a single composition. Not only could this be formulated so as to contain the most appropriate amount of alum for the sizing components present, but also the most effective and therefore economical use of all the materials would follow. It has long been thought that this highly desirable goal could not be achieved, except perhaps only in certain somewhat exceptional cases, because of the fundamental incompatibility of sizing agents and alum. Since the basic purpose of the latter is to destroy the stability of the former, it is not to be expected that a single composition could combine the two and remain in a stable and usable condition.